1. Field of the Invention
The present invention relates to a catalyst for producing carbon nanotubes, and more particularly to a catalyst for producing carbon nanotubes with a large specific surface area and carbon nanotubes produced using the catalyst.
2. Description of the Related Art
Carbon nanostructures (CNSs) refer collectively to nano-sized carbon structures having various shapes, such as nanotubes, nanohairs, fullerenes, nanocones, nanohorns, and nanorods. Carbon nanostructures can be widely utilized in a variety of technological applications because they possess excellent characteristics.
Particularly, carbon nanotubes (CNTs) are tubular materials consisting of carbon atoms arranged in a hexagonal pattern and have a diameter of approximately 1 to 100 nm. CNTs exhibit insulating, conducting or semiconducting properties depending on their inherent chirality. CNTs have a structure in which carbon atoms are strongly covalently bonded to each other. Due to this structure, CNTs have a tensile strength approximately 100 times that of steel, are highly flexible and elastic, and are chemically stable.
CNTs are divided into three types: single-walled CNTs (SWCNTs) consisting of a single sheet and having a diameter of about 1 nm; double-walled CNTs (DWCNTs) consisting of two sheets and having a diameter of about 1.4 to about 3 nm; and multi-walled CNTs (MWCNTs) consisting of three or more sheets and having a diameter of about 5 to about 100 nm.
CNTs are being investigated for their commercialization and application in various industrial fields, for example, aerospace, fuel cell, composite material, biotechnology, pharmaceutical, electrical/electronic, and semiconductor industries, due to their high chemical stability, flexibility and elasticity. However, CNTs have a limitation in directly controlling the diameter and length to industrially applicable dimensions for practical use owing to their primary structure. Accordingly, the industrial application and use of CNTs are limited despite their excellent physical properties.
CNTs are generally produced by various techniques, such as arc discharge, laser ablation, and chemical vapor deposition. However, arc discharge and laser ablation are not appropriate for mass production of CNTs and require high arc production costs or expensive laser equipment. Chemical vapor deposition using a vapor dispersion catalyst has the problems of a very low synthesis rate and too small a size of final CNT particles. Chemical vapor deposition using a substrate-supported catalyst suffers from very low efficiency in the utilization of a reactor space, thus being inappropriate for mass production of CNTs. Thus, studies on catalysts and reaction conditions for chemical vapor deposition are currently underway to increase the yield of CNTs.
A need also exists for CNTs that have a small diameter and can be readily dispersed in and mixed with polymers during compounding with the polymers to manufacture composite materials with improved physical properties.